COMPARING GROUND PENETRATING RADAR SURVEY (GPR) CONFIGURATIONS FOR IDENTIFYING GRAVES, GEORGE AND ADDIE GIDDENS CEMETERY, OPELIKA, AL

Recent interest in locating and preserving unmarked burials of enslaved African Americans has increased the need for non-invasive geophysical techniques and efficient methodologies. In this study, GPR was used to locate unmarked burials in the George and Addie Giddens Cemetery and compare existing methodologies to determine the most effective methods to locate these burials and assist in geophysical interpretation. Bilateral survey methods were compared against unidirectional survey methods and were found to introduce additional errors in uneven topographic terrain. Datasets were collected at both 1-meter and 0.25-meter intervals in order to test the effectiveness of these different spacings. The 1-meter intervals were found to be insufficient for locating unmarked burials and burial shafts in the George and Addie Giddens Cemetery. Data collection in uneven topography covers a greater distance than originally gridded, which creates errors that are propagated by bilateral collection methods as the neighboring datasets will not match in the 3D grid files created. Unidirectional collection minimized the error as it matched the terrain more closely when approached from the same direction. Data collection at 1-meter intervals failed to locate as many potential burial sites as 0.25-meter intervals possibly due to the nature of the cemetery, in which many burials may be highly decomposed or lack coffins and are located sporadically within the cemetery. Using a unidirectional survey pattern in non-flat terrain is important for minimizing errors and 0.25-meter intervals is a more effective methodology for locating unmarked graves.